LIGHT-ACTIVATED GUANOSINE-TRIPHOSPHATASE IN MUSCA EYE MEMBRANES RESEMBLES THE PROLONGED DEPOLARIZING AFTERPOTENTIAL IN PHOTORECEPTOR CELLS
LIGHT-ACTIVATED GUANOSINE-TRIPHOSPHATASE IN MUSCA EYE MEMBRANES RESEMBLES THE PROLONGED DEPOLARIZING AFTERPOTENTIAL IN PHOTORECEPTOR CELLS
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DOI：
10.1073/pnas.82.20.7116
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发表时间：
1985-01-01
影响因子：
11.1
通讯作者：
MINKE, B
中科院分区：
文献类型：
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作者：
BLUMENFELD, A;ERUSALIMSKY, J;MINKE, B
在电生理实验的指导下，利用光依赖的GTP酶(EC 3.1.5.1)活性的测量来研究鸟嘌呤核苷酸结合蛋白在苍蝇光转导中的参与。蝇眼的无细胞膜制剂对蓝光的反应是GTP水解酶活性的10-20倍。这种光依赖的GTP酶对GTP的Km较低(0.5µm)，并能有效地被鸟苷(5‘’.fwdarw)抑制。3)-1-硫代三磷酸和鸟苷5‘’-[β-γ-亚氨基]三磷酸，但不是腺苷5‘’-[β-伽马-亚氨基]三磷酸和三磷酸腺苷。强光下测得的GTP酶活性的作用光谱与变视紫质的光平衡光谱非常相似。在蓝光(<；480 nm)照射下，GTP酶在黑暗中保持高活性至少60分钟。同样，在完整细胞中，视紫红质到后紫质的转换导致了延长的后电位(PDA)。红光(>；570 nm)将变视紫质转化为视紫红质后，持续的GTPase活性(如PDA)被抑制到非照明膜的低基础活性，而在红光照射下，部分GTPase活性保持不变。在黑暗中持续的GTPase活性的大小，如PDA，以超线性的方式依赖于色素转换量。因此，蝇类膜制剂的GTPase活性对光色素转换的依赖类似于在完整的蝇类光感受器中测量的PDA的诱导和抑制。这些发现表明，鸟嘌呤核苷酸结合蛋白是导致受体电位和PDA产生的事件链的一部分。
Measurement of light-dependent GTPase (EC 3.1.5.1) activity in a paradigm guided by electrophysiological experiments was used to examine the involvement of a guanine nucleotide binding protein in fly phototransduction. Cell-free membrane preparations of Musca eyes responded to blue light by a 10- to 20-fold increase in GTP-hydrolyzing activity. This light-dependent GTPase had a low Km for GTP (0.5 .mu.M) and was effectively inhibited by guanosine (5'' .fwdarw. O3)-1-thiotriphosphate and guanosine 5''-[.beta.-.gamma.-iminio]triphosphate but not by adneosine 5''-[.beta.-.gamma.-imino]triphosphate and ATP. The action spectrum of GTPase activity measured with intense light resembled closely the photoequilibrium spectrum of metarhodopsin. After illumination with blue (< 480 nm) light, which converted rhodopsin to metarhodopsin, the GTPase remained highly active for at least 60 min in the dark. Similarly, rhodopsin-to-metarhodopsin conversion in intact cells induced a prolonged afterpotential (PDA). The persistent GTPase activity (like the PDA) was suppressed to the low basal activity of the unilluminated membranes after conversion of metarhodopsin to rhodopsin with red light (> 570 nm), whereas during illuminatioun with red light, some GTPase activity was maintained. The magnitude of the persistent GTPase activity in the dark, like the PDA, depended in a supralinear manner on the amount of pigment conversion. Thus, the dependence of GTPase activity of Musca membrane preparations on photopigment conversion resembles the induction and suppression of the PDA measured in intact photoreceptors of Musca. These findings indicate that a guanine nucleotide binding protein is part of the chain of events leading to both the generation of the receptor potential and the PDA.